1. Field of the Invention
The present invention relates to a method and system for determining video program system (VPS) signals detected from television signals.
2. Description of the Related Art
It has been put to practical use to allocate a VPS signal to each of television programs and to detect and determine the VPS signal (see FIG. 1A), which has been superimposed on a specific line in a vertical-blanking interval of a television signal prior to the start of broadcasting of the program, in order to control various types of TV signal receiving equipment. As shown in FIG. 1B, the VPS signal is represented by 1-15 word data, and the word data (word numbers 11-14) in current use includes the broadcasting data (the month, day and hour), the nationality code of a broadcasting station, a program source code, etc, which are previously published in a television program guide and assigned to each of programs. For example, by means of the VPS signal a TV is turned on and a video tape recorder (VTR) is controlled in a recording mode.
To control TV signal receiving equipment by means of VPS signals as described above, this receiving equipment decodes a received VPS signal and determines whether or not a program source code obtained by the decoding corresponds to a preset program source code. Therefore, it is necessary for the receiving equipment to accurately detect the VPS signal. However, by mixed with noise, the VPS signal may become difficult to detect.
A example of a determination circuit for VPS signals is shown in German Offenlegungsschrift (Document open for inspection) DE-OS.3,511,737. The determination circuit includes a memory, a comparing circuit, and a counter. A detected VPS signal is stored in the memory, compared with a next detected VPS signal. When the VPS signal stored in the memory coincides with the next detected VPS signal, the counter is incremented by one. When no coincidence occurs between these VPS signals, the counter is reset. By the above process, a count value of the counter is obtained when the same VPS signal is successively detected. When a predetermined count value is counted by the counter, the determination circuit determines that the VPS signals correspond to a program being broadcast. The another samples of a known determination circuit for VPS signals is shown in FIG. 2. The determination circuit determines by using the majority of VPS signals, and includes input buffer 16, counters 17a, 17b and 17c, no-signal counter 18, determination process circuit 19 and controller 20. Controller 20 is constructed of a central processing unit (CPU) and the like and controls the timing of access to input buffer 16. The determination of VPS signals is performed in accordance with a flowchart as shown in FIG. 3.
In FIG. 3, when a VPS signal determination process is started, a VPS signal is detected from a television signal and input into input buffer 16 at a specified timing by a control signal output from controller 20 (step S1). The VPS signal input into input buffer 16 is regarded as a VPS signal for a program A, counter 17a is incremented by one (step S5). Determination process circuit 19 determines whether or not a next VPS signal input into input buffer 16 coincides with the VPS signal for the program A (step S2). In step S2, when the next VPS signal corresponds to the program A, counter 17a is incremented by one (Step S5). In step S2, if the next VPS signal does not correspond to the program A, the next VPS signal is regarded as a VPS signal for a program B, counter 17b is incremented by one (step S6). Similarly, determination process circuit 19 determines whether or not a new VPS signal input into input buffer 16 coincides with the VPS signal for programs A or B (step 2, step S3). When the new VPS signal corresponds to the program A, counter 17a is incremented by one (step S5). When the new VPS signal corresponds to the program B, counter 17b is incremented by one (step S6). If the new VPS signal does not correspond to the programs A and B, the new VPS signal is regarded as a VPS signal for a program C, counter 17c is incremented by one (step S7). When a VPS signal input into input buffer 16 corresponds to the program C (step S4), step S7 is performed. When the VPS signal input into input buffer 16 does not correspond to any one of programs A, B and C, for example, when the VPS signal is a no-signal, no-signal counter 18 is incremented by one (step S8).
The above process is performed at regular intervals and continued for a predetermined period (step S9). When the input of the VPS signal into input buffer 16 for the predetermined period is completed (step S9), step S10 is then performed.
In step S10, the VPS signal is detected which corresponds to a counter having a maximum count value among counters 17a, 17b and 17c and no-signal counter 18. For example, when the count value of counter 17a is maximum, the VPS signal for program A has been detected most frequently during the predetermined period. As a result, the conventional determination circuit determines that a program being broadcast is A.
However, the conventional determination procedure for the VPS signals involves the following problems.
For example, when television signals are received unstably, VPS signals will also become unstable and thus may not be determined. In such a case, the determination procedure as shown in FIG. 3 will fail to determine any of VPS signals corresponding to programs in each of steps S2, S3 and S4, increasing the count value of no-signal counter 18. For example, if normal VPS signals are detected only two times during five determination processes, then no-signal counter 18 will count three times. Thus, determination circuit would be determined that the VPS signal is not superimposed upon a television signal being received.
From the above, an apparatus is desired which is capable of accurately detecting and determining VPS signals from received television signals.